1. Field of the Invention
The invention relates to methods of oligomerizing olefins over a boron trifluoride catalyst together with a promoter, and more particularly relates to methods of oligomerizing a mixture of predominantly low molecular weight alpha olefins over a boron trifluoride catalyst in the presence of an organic protonic promoter.
2. Description of Related Methods
Nearly all of the patents issued on olefin oligomerization have involved alpha olefins. For example, see U.S. Pat. No. 3,410,925 to Eby, et al. in which alpha olefins are mixed with alkylatable aromatic hydrocarbons over a Friedel-Crafts catalyst to form an alkylation sludge which is then mixed with olefins having 3 to 18 carbon atoms which are also passed over the catalyst to produce olefin dimers. U.S. Pat. No. 3,652,706 to Saines, et al. describes the polymerization of alpha olefins having 2 to 20 carbon atoms over a Friedel-Crafts metal halide catalyst plus a hydrogen form of mordenite to produce compounds having a molecular weight between 700 and 2,500. Production of a gasoline fuel composition is described in U.S. Pat. No. 3,749,560 to Perilstein which occurs by reacting a mixture of mono olefins over a Friedel-Crafts catalyst heated to a temperature around 145.degree. C. to produce oligomers having molecular weights between 350 to 1,500. Also, U.S. Pat. No. 3,149,178 to Hamilton, et al. reveals an improved method for making polymerized olefin synthetic lubricants via a particular distillation technique of oligomers made from alpha mono olefins using a Friedel-Crafts catalyst. Alpha olefins having six to twelve carbon atoms may be dimerized in the presence of a Friedel-Crafts catalyst according to the method described in U.S. Pat. No. 4,172,855 to Shubkin, et al.
It is also known that the term "Friedel-Crafts catalysts" includes boron trifluoride among other metal halide-type Lewis catalysts, see Kirk-Othmer Encyclopedia of Chemical Technology, Third Edition, Vol. 11, pg 292. Boron trifluoride has also been known to polymerize olefins, as seen in F. Albert Cotton, et al., Advanced Inorganic Chemistry: A Comprehensive Text, Interscience Publishers, 1962, p. 191.
A number of patents have also used BF.sub.3 to oligomerize olefins. For example, British Pat. No. 1,323,353 describes the use of wax cracked alpha olefins as precursors for synlube fluids. U.S. Pat. No. 2,780,664 to Serniuk describes the reaction of conjugated dienes with mono olefins over BF.sub.3 promoted by an ether mixed with a halo alkane diluent at a temperature from -30.degree. to 100.degree. C. to produce oligomers suitable for drying oils. Alpha olefins having from 5 to 20 carbon atoms are oligomerized using BF.sub.3 plus an alcohol or water promoter as described in U.S. Pat. No. 3,382,291 to Brennan. In this patent, BF.sub.3 and a mixture of BF.sub.3 plus the promoter complex are introduced in two separate streams. Another U.S. Pat. No. by Brennan, 3,742,082, concerns the dimerization of alpha olefins via BF.sub.3 which is promoted with phosphoric acid or water at a temperature from 100.degree. to 150.degree. C. U.S. Pat. No. 3,763,244 to Shubkin, describes the oligomerization of n-alpha olefins having 6 to 16 carbon atoms over BF.sub.3 promoted with water, at a temperature between 10.degree. and 60.degree. C. where it is preferred that BF.sub.3 is added continuously.
Yet another U.S. Pat. No. to Brennan, 3,769,363 describes the oligomerization of olefins having 6 to 12 carbon atoms using BF.sub.3 with a carboxylic acid promoter having at least 3 carbon atoms at a temperature between 0.degree. and 20.degree. C. to produce olefins heavy in trimer form. U.S. Pat. No. 3,780,128 also to Shubkin relates to the oligomerization of alpha olefins having 6 to 16 carbon atoms in which BF.sub.3 is employed in a molar excess of alcohol. U.S. Pat. No. 3,876,720 to Heilman, et al. describes a two-step procedure by which alpha olefins having 8 to 12 carbon atoms are converted to vinylidene olefins which are then reacted over a 1:1 molar complex of BF.sub.3 and alcohol to produce oligomerized vinylidene olefins. A method for oligomerizing both short and long chain alpha olefins having from 14 to 20 carbon atoms simultaneously over BF.sub.3 with an alcohol or water promoter at 0.degree. to 60.degree. C. with a monomer recycle is described in U.S. Pat. No. 4,225,739 to Nipe, et al. There is also U.S. Pat. No. 4,263,465 to Sheng, et al. which describes a two-step process for reacting 1-butene with a higher alpha olefin over BF.sub.3 in the presence of a proton donor at a temperature from -30.degree. to 50.degree. C. to produce an oligomer having 8 to 18 carbon atoms. The intermediate oligomer is reacted with other higher alpha mono olefins over the same catalyst system from -30.degree. to 60.degree. C. to produce oligomers having 20 to 40 carbon atoms. For more information on BF.sub.3 -catalyzed oligomerization of alpha olefins, see Brennan, "Wide-Temperation Range Synthetic Hydrocarbon Fluids," Ind. Eng. Chem. Prod. Res. Dev. 1980, Vol. 19, pp 2-6 and Shubkin, et al., "Olefin Oligomer Synthetic Lubricants: Structure and Mechanism of Formation," Ind. Eng. Chem. Prod. Res. Dev. 1980, Vol. 19, pp 15-19.
U.S. Pat. No. 4,213,001 reveals a method of homopolymerizing an alpha olefin by utilizing boron trifluoride under pressure in the presence of a suspended particulate absorbent material. The absorbent material may be silica, alumina, magnesia, zirconia, activated carbon, the zeolites, silicon carbon, silicon nitride, titania, thoria, porous polyvinyl alcohol beads, porous polyethylene glycol beads and the like.
Additional methods in this field include that of U.S. Pat. No. 4,045,507 which involves a multi-stage, continuous process for polymerizing alpha olefins having 5 to 14 carbon atoms in the presence of boron trifluoride and a co-catalyst. A process involving the copolymerization of propylene or propylene plus higher alpha olefins with small amounts of ethylene in the presence of a vanadium-containing catalyst, an aluminum-containing catalyst and a Friedel-Crafts catalyst is described in U.S. Pat. No. 4,182,922 and may be of particular interest. U.S. Pat. No. 4,263,465 involves the preparation of a low viscosity synthetic lubricant by polymerizing 1-butene to an oligomer containing a number average of about 8 to 18 carbon atoms and copolymerizing the oligomer with an alpha-mono olefin having 8 to 18 carbon atoms to produce a copolymer having an average of about 20 to 40 carbon atoms.
U.S. Pat. No. 4,300,006 issued on Nov. 10, 1981. It describes a process for producing a hydrocarbon oil by contacting a mixture of alpha and at least 50 weight percent internal olefins with a boron trifluoride dimerization catalyst. However, the productivity of useful products from the process revealed in U.S. Pat. No. 4,300,006 is quite low. For example, an alkane diluent is found to be necessary in the process described therein. When the lights and heavies are distilled out as required by the method, little useful product results. Further, this method requires a much longer reaction time and a higher catalyst concentration than desired. It would be beneficial if a method for producing synthetic lubricants could be devised which would overcome the aforementioned disadvantages.
Also of interest is U.S. Pat. No. 4,214,112. It discloses a process for producing an olefin oligomer which involves polymerizing olefins having not less than 6 carbon atoms in the presence of a specified catalyst system. The system consists of an aluminum halide, a polyhydric alcohol derivative and a nickel compound or a cobalt compound. The nickel and cobalt compounds are listed as nickel monoxide, trinickel tetroxide, nickel sequioxide, nickel hydroxide, nickel sulfide, nickel sulfate, nickel acetate, nickel oleate, nickel stearate, nickel diatomaceous earth, nickel chloride, nickel acetylacetonate, nickel peroxide, cobalt carbonate, dicobalt octacarbonyl, cobalt chloride, cobalt nitrate, cobalt oxide, cobalt hydroxide, cobalt sulfide, cobalt sulfate, cobalt acetate, cobalt oleate, cobalt acetylacetonate, etc. and combinations thereof. The compounds used in the examples therein are nickel oxide, nickel chloride, nickel oleate, nickel carbonate and cobalt chloride.
In the field of oligomerizing olefins for synthetic lubricants, it is a continual problem to produce olefins having low viscosities at room temperature and below but which have a high viscosity index and low volatility.